Direct current (DC) diode sputtering is not efficient. That is, it is not efficient by the standard of the fraction of species backscattered from the target (sputtered) that are captured on a substrate surface. This inefficiency is attributable to the fact that higher working pressures (>10 mTorr) are required to facilitate the collisional frequency that initiates an avalanche-effect supply of ionizing electrons. Unfortunately, at elevated working pressures, the sputtered species (adsorbate) are readily scattered by the working gas atoms and ions. As a result, a diminishing portion of the working gas atoms and ions actually makes it to the substrate. The balance is later found deposited upon the shielding and other chamber surfaces.
Magnetron solutions are the standard in the industry; however, while they commonly offer high deposition rates at lower pressure, and full surface erosion, they are limited to processing at ˜0.5 Pa (Ar), and deliver an adsorbate that is neutral. Unbalancing the magnetic strength of the magnetron is effective at increasing the ionization fraction (adsorbate), but requires higher ignition pressure. Also, since the band of highly ionizing electrons is confined to a narrower spatial distribution, use of this configuration typically exhibits lower than desired target utilization.
Radio frequency magnetrons (rf-magnetrons) are effective in increasing the ionization cross section, thereby reducing the critical pressure for sputtering, but require expensive setups (power supplies, matching boxes, etc.) and are not very compatible with changing loads (e.g., as in a pass-by sputter system).
In this context, a general solution is sought that offers very low pressure operation (<0.1 Pa) and high plasma density with ionic flow toward the substrate. A specific solution is also sought for processing diamond-like carbon (DLC). In the specific case of DLC, one typically observes a high concentration of graphitic carbon. It is well known that traditional sputtering including magnetron setups yield a predominantly neutral adsorbate. Without a highly ionized sputter and commensurately high electron density, the resultant plasma is not easily controlled with electron optics and electrostatic bias fields. This control of the adsorbate is richly sought after due to the incumbent abilities afforded the thin film designer in terms of film bombardment and control of the incident energy.
Filtered Cathodic Arc (FCA) is a known method by which DLC films are viably fabricated. FCA works by impinging a high current arc from a cathode made of the target material to an engineered anode. Highly localized energy then causes explosive evaporation with a large flux of ionizing electrons. This ejected plasma is then directed through a filter via magnetic fields. The evaporation event leads to a high degree of particulate formation via cavitation of the surface. These particulates are too heavy to follow the plasma through the various twist and turns in the applied magnetic field and thus are captured ex-situ to the work environment. However, a finite number of particles do make it through to the substrate mostly due to reflection from the various surfaces offered by the filter. As filtering is increased, the transfer efficiency noted as the fraction of those ions entering the filter to the total created, □=Ii/If, is seldom reported greater than 5%. For this reason, it is found to be intractable to achieve deposition rates approaching 1 nm/s without very large input powers (>3 kW). Also, because the transfer efficiencies are so low, the amount of starting material is quite large depending on the desired “uptime” for continuous processing demands.
There is no currently available technology capable of simultaneously increasing the density of thin film carbon while maintaining compatibility with volume manufacturing rigors in industries including recording media for hard disc drives.